Controlling Isomerization Selectivity in Chiral, Photochromic N,C-Chelate Organoboron Systems with Extended π-Conjugation.

Alkyne-functionalized chelate boron compounds with extended π-conjugation on one of the aryl groups attached to boron display thermally reversible and regioselective isomerization on the more delocalized substituent, forming base-stabilized boriranes with an intense color. Linking two of such boron chromophores through a 1,4-phenylene spacer via ethynyl moieties leads to photochemically inert molecules, while connecting them by a nonconjugated silicon bridge yields photochromic systems capable of switching at a single boron center.